Investigating slab edge kinematics through seismological data: The northern boundary of the Ionian subduction system (south Italy)

•Seismic analyses characterize present kinematics of the Ionian slab northern edge.•We evidence seismological signatures of the continuous-slab edge.•Shallow signatures of STEP fault lateral migration at the slab edge are found.•Seismic constraints to the modelling of the Ionian subduction system are furnished.

An integrated analysis of seismotomography models, earthquake spatial distribution and focal mechanism solutions has been performed in the still poorly constrained region marking the northern boundary of the Ionian subducting slab (south Italy). In this area, research findings related to the continuous- vs detached-slab transition are diffused on a wide sector running from central Calabria to the southern Apennines tip and different locations of a subduction-transform edge propagator (STEP) have also been proposed in the recent literature. We present seismic data and analyses aimed to investigate the location of the northern edge of the in-depth continuous slab and the present-day kinematics of the concerned boundary region by also focusing on the possible clues of STEP fault activity. We used both standard linearized and non-linear probabilistic methods to locate, in a recently developed shallow-to-intermediate 3D velocity model, the seismicity that occurred between 1997 and 2012 at the Ionian slab northern boundary. Earthquake kinematics have also been investigated by integrating high-quality focal mechanisms selected from the literature with 70 waveform inversion solutions obtained in the present study.The results allow to identify in central Calabria the northern edge of the in-depth continuous slab and just north of it a ca. 100 km-wide deformation zone reflecting lateral STEP migration in the slab edge area. The migration likely indicates an alternation of tear propagation along a slab edge and slab break-off progressively reducing the lateral extension of the subduction zone. In this framework, the recent seismicity seems also to suggest the possible location of an incipient shallow slab break-off beneath central Calabria.